Using CGDisplayStream to detect window movement

Question

I want to detect when a window is being moved in real time and figured that CGDisplayStreamCreate etc. should provide just that. But I'm having difficulty deciding which window is being moved when my CGDisplayStreamFrameAvailableHandler is called. Is there a direct way to match the updated rects with with an app and its windows?

Answer 1

CGDisplayStream cannot tell you which applications/windows are responsible for a given screen update. You might be able to use another API like Accessibility to determine window locations and then guess which of the kCGDisplayStreamUpdateMovedRects corresponds to each window, but that will not be very reliable. If you're going to go the route of Accessibility, you may as well use Accessibility notifications for window move events: How can my app detect a change to another app's window? .

If you also need the pixel contents of the windows when they are moving, then you'll need to do some unfortunate time alignment between CGDisplayStream and Accessibility callbacks.